P m n ( t , t + Δ t ) ≡ ρ m m ( t ) − ρ m m ( t + Δ t ) ρ m m ( t ) = max [ 0 , − 2 Δ t ℏ ρ m m ℜ ( ρ m n ) d m n ⋅ v ]
Δ t
Numerical problems may occur due to the (near) divergence of the nonadiabatic coupling tensor elements, thus enforcing very small time steps.
Light Particle Nonadiabatic Probability 1
FSSH-1 probability for a nonadiabatic transition of the light particle(s) subsystem, induced by the heavy particle(s) dynamics